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Commit af7f8721 authored by Ingo Molnar's avatar Ingo Molnar
Browse files

x86/fpu: Document fpu__unlazy_stopped() 



Explain its usage and also document a TODO item.

Reviewed-by: default avatarBorislav Petkov <bp@alien8.de>
Cc: Andy Lutomirski <luto@amacapital.net>
Cc: Dave Hansen <dave.hansen@linux.intel.com>
Cc: Fenghua Yu <fenghua.yu@intel.com>
Cc: H. Peter Anvin <hpa@zytor.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Oleg Nesterov <oleg@redhat.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: default avatarIngo Molnar <mingo@kernel.org>
parent 4c138410

arch/x86/kernel/fpu/core.c

+21 −4
Original line number Diff line number Diff line
@@ -284,10 +284,27 @@ int fpstate_alloc_init(struct task_struct *curr) 
EXPORT_SYMBOL_GPL(fpstate_alloc_init);



/*

 * The _current_ task is using the FPU for the first time

 * so initialize it and set the mxcsr to its default

 * value at reset if we support XMM instructions and then

 * remember the current task has used the FPU.

 * This function is called before we modify a stopped child's

 * FPU state context.

 *

 * If the child has not used the FPU before then initialize its

 * FPU context.

 *

 * If the child has used the FPU before then unlazy it.

 *

 * [ After this function call, after the context is modified and

 *   the child task is woken up, the child task will restore

 *   the modified FPU state from the modified context. If we

 *   didn't clear its lazy status here then the lazy in-registers

 *   state pending on its former CPU could be restored, losing

 *   the modifications. ]

 *

 * This function is also called before we read a stopped child's

 * FPU state - to make sure it's modified.

 *

 * TODO: A future optimization would be to skip the unlazying in

 *       the read-only case, it's not strictly necessary for

 *       read-only access to the context.

 */

static int fpu__unlazy_stopped(struct task_struct *child)

{